Device and method for reading an image plate

ABSTRACT

A device and method for reading an exposed imaging plate generate read-out light and utilize a deflection unit to direct the read-out light in a scanning movement over the imaging plate. The deflection unit has a micromirror to deflect impinging read-out light towards the imaging plate. The micromirror can swivel about a first swivel axis and about a second swivel axis distinct from the first. A detector unit detects fluorescent light emitted from the imaging plate at locations where the read-out light impinges. An evaluating unit evaluates signals received from the detector unit and builds up an image that is stored in the imaging plate. The evaluating unit takes into account, when evaluating the signals received from the detector unit, that points on the imaging plate are subjected to the read-out light variably often and/or for variable time lengths while the micromirror oscillates about the first and the second swivel axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to and thebenefit of, co-pending U.S. application Ser. No. 14/283,994 filed on May21, 2014 and entitled “Device and Method for Reading an Imaging Plate”,which is a continuation of International application PCT/EP2012/004017,which was filed on Sep. 26, 2012 and which claimed priority to and thebenefit of German patent application Ser. No. 102011119049.3 filed Nov.22, 2011. The full disclosures of these earlier applications are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a device and a method for reading an exposedimaging plate.

2. Description of Related Art

In X-ray technology, particularly in dental X-ray technology, imagingplates are used nowadays for the purpose of recording X-ray images.These imaging plates include a phosphor material which has been embeddedin a transparent matrix. As a result, so-called storage centres arise,which can be brought into excited metastable states by incident X-raylight. If such an imaging plate is exposed in an X-ray apparatus, forexample for the purpose of recording the dentition of a patient, theimaging plate contains a latent X-ray image in the form of excited andnon-excited storage centres.

For the purpose of reading the imaging plates, the latter are scannedwith read-out light, point by point, in a scanner, as a result of whichthe metastable states of the excited storage centres are brought into astate that relaxes rapidly, emitting fluorescent light. This fluorescentlight can be registered with the aid of a detector unit, so that theX-ray image can be made visible with appropriate evaluating electronics.

Conventional scanners, such as a drum scanner for example, conduct theimaging plate along a cylindrical surface across a read-out gap. In theinterior of the cylindrical surface a rotary mirror has been provided byway of deflection unit, which generates a circumferential read-out beam.The latter falls through the read-out gap onto the imaging plate andreads the latter in pointwise manner. Meanwhile the imaging plate isconducted past the read-out gap by a mechanical drive, so that theentire surface of the imaging plate is registered.

With such a drum scanner, particularly in the dental field in whichmostly small-format imaging plates come into operation, it isdisadvantageous that the imaging plate has been arranged only along asmall region of the periphery of the cylinder. For a large proportion ofthe read-out time the read-out beam therefore circulates within a regionwhere no imaging plate is present, so that, on average, the read-outbeam actually impinges on the imaging plate only during approximately10% of the read-out time. This results in unnecessarily long read-outtimes.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a device and amethod with which the read-out efficiency has been improved.

With regard to the device, this object is achieved by a device that isconfigured to read an exposed imaging plate, comprises a light-sourcethat generates read-out light. A deflection unit directs the read-outlight in a scanning movement over the imaging plate. The deflection unitcomprises a micromirror that deflects impinging read-out light towardsthe imaging plate. The micromirror swivels about a first swivel axis andabout a different second swivel axis. The micromirror oscillates with afirst frequency about the first swivel axis and simultaneously with adifferent second frequency about the second swivel axis. A detector unitdetects fluorescent light which is emitted from the imaging plate atlocations where the read-out light impinges.

It has been recognised that with a controllable mirror that is capableof being swivelled back and forth, the read-out light can be guided insuch a way that most of the time it falls onto the imaging plate. As aresult, the time that is needed overall for reading an imaging plate isreduced.

The micromirror may, in particular, take the form of a MEMS micromirror(MEMS: microelectromechanical system). Characteristic of MEMS technologyis the integration of mechanical elements, actuators and electronics ona common substrate, with manufacture being undertaken in a mannersimilar to that in the case of processors and memory chips, andincluding the application of layers of material and subsequent selectiveetching. MEMS micromirrors are very reliable and, by reason of their lowmass, react very quickly to drive signals, so that high deflectionspeeds can be obtained.

By virtue of a deflection about two axes, a two-dimensional imagingplate can be scanned even without relative motion between the deflectionunit and the imaging plate. The two axes in this case havepreferentially been arranged parallel to the edges of the mostlyrectangular imaging plate.

In one embodiment, the mirror is capable of being swivelled about thetwo swivel axes continuously between two end positions. By virtue of acontinuous swivelling capacity along the swivel axes, the micromirror isable to scan an uninterrupted scan line on the imaging plate.

A MEMS micromirror is usually provided with a cardanic suspension, thesuspension points of which take the form of solid joints. As a result,the micromirror with the solid joints forms a system capable ofoscillating, which exhibits a natural frequency for each degree offreedom. If the micromirror is driven at, or close to, naturalfrequency, then oscillation amplitudes are obtained that are as large aspossible with as little expenditure of energy as possible.

The mirror may have different natural frequencies about the two swivelaxes. In this way, differing oscillation frequencies in differingscanning directions can be obtained with low expenditure of energy.

A predetermined pattern may be scanned on the imaging plate with theread-out light, whereby the pattern may cover the entire imaging platewith uniform density. By virtue of a uniform density in the course ofthe scanning of the imaging plate, the signal-to-noise ratio and theresolution of the X-ray image that has been read are approximatelyconstant over the entire imaging plate.

If a control unit drives the mirror in such a way that a Lissajousfigure or curve on the imaging plate is scanned with the read-out light,then a complete scanning of the entire imaging plate may be obtained. Inparticular, the micromirror and the imaging plate in this case may havebeen arranged relative to one another in such a way that the Lissajousfigure or curve extends beyond the edges of the imaging plate. The partof the pattern projecting beyond one of the edges preferentiallycorresponds to between 5% and 15% of the dimension of the imaging plateperpendicular to this edge.

In the case of the Lissajous figures or curves the control unit may beable to drive the mirror about the two swivel axes at frequencies thatcorrespond to a large, preferentially variable, preferentially integral,multiple of a base frequency, in particular to 0.5 times the desirednumber of lines or the number of columns of the image, and/or thatdiffer slightly from one another from such an integral multiple, inparticular by approximately 10% of the lower frequency. The slightdifference may also amount to only approximately 2% of the lowerfrequency.

For example, frequencies of 30 Hz and 40 Hz may be used, in which casethe base frequency would then be 10 Hz, and a ratio of 3:4 results. Ifthe two frequencies or frequency multiples of the Lissajous figure orcurve differ slightly, then a moving Lissajous figure or curve isscanned. ‘Moving’ here means a Lissajous figure or curve changing in amanner similar to a beat. As a result, the entire imaging plate can bescanned.

Another method for scanning the entire imaging plate consists in usingfrequencies being large integral multiples of one another, in particular0.5 times the desired number of lines or number of columns of the image.‘Large’ in this connection means, in particular, that the twofrequencies at which the mirror is driven differ by more than a factorof more than 250, preferentially more than 500.

An evaluating unit may be connected to the detector unit, which in thecourse of evaluating takes account of the fact that, by virtue of theoscillatory motion of the mirror, various points of the imaging plateare scanned variably often and/or for variably long times, in particularby means of a position dependent correction factor.

In the course of the scanning of Lissajous figures or curves and someother patterns, some points are scanned repeatedly, and other pointsonce only. As a result, storage centres that have remained in theexcited state are read out additionally in the course of the laterscanning. The diminution, increasing after each further scanning of apoint, of the excited storage centres can, for example, be taken intoaccount by a weighted averaging. However, the variable scanning ofvarious points may result in a locally variable signal-to-noise ratio.For this reason, the evaluating unit may, in the course of evaluating,have recourse to a correction table that was created on the basis ofcalibration measurements.

The Lissajous figures or curves can be simulated mathematically, and theregistered intensities can be corrected accordingly. Better, however, isa calibration on the basis of calibrating imaging plates, for example auniformly exposed imaging plate. Once this has been read, theintensities obtained are converted into correction values which aresaved in the correction table.

The device may include a sync detector, preferentially a photodiode,with which the read-out light can be detected at a predeterminedscanning location in order to synchronise the evaluating unit with themotion of the mirror. In this way, the registration of the detectorsignal can be synchronised by the evaluating unit, as needed, with thescanning motion of the read-out light beam.

A control unit may be provided, with which periodic pulses can begenerated which excite the mirror to oscillate. In this connection theperiodicity, the pulse width, the pulse shape and/or the pulse heightmay be variable, in order to influence the excited oscillation amplitudeand/or oscillation frequency of the mirror, as a result of whichdiffering patterns can be generated.

But a control unit may also have been provided, with which the mirrorcan be driven with a sawtooth voltage or with a delta voltage. As aresult, the imaging plate can be read uniformly.

Several mirrors may also have been arranged in a mirror array. In thiscase, differing mirrors may be assigned to differing regions of theimaging plate. For example, with two biaxial mirrors two Lissajousfigures or curves arranged side by side can be generated in succession,in order to read larger imaging plates completely.

The imaging plate and the deflection unit may be capable of movingrelative to one another, the imaging plate preferentially beingconducted past the deflection unit. In this way, large-format imagingplates can be read. In the case where use is made of an only uniaxialmirror, the relative motion is necessary in order to be able to read theimaging plate in two dimensions.

A control unit may have been provided, with which the mirror is capableof being driven in stepwise manner, so that the imaging plate can beread out, pixel by pixel, in a matrix. ‘Stepwise’ in this connectionmeans that the mirror comes to a state of rest after any change in theposition of tilt. This enables the read-out with a constantsignal-to-noise ratio.

A maximal read-out range may have been defined, in which the imagingplate is capable of being scanned solely by deflecting the read-outlight. Furthermore, the device may include an erasing appliance withwhich erasing light can be directed onto the imaging plate after thereading of the imaging plate in an erasing region, the erasing region onthe imaging plate being at least as large as the read-out region. If theread-out region and the erasing region coincide, the imaging plate canbe erased at the same location at which it is read, so that no drivemeans for conveying in the direction of an erasing appliance arenecessary.

According to a further embodiment, the read-out light may deflected bythe deflection unit may generate an impingement spot on the imagingplate, and the erasing appliance includes a switching element with whichthe impingement spot can be enlarged for the purpose of erasing theimaging plate, whereby the read-out light is used as erasing light.

If, for the purpose of erasing the imaging plate, use is made ofcomponents that are needed anyway for the purpose of reading, additionalcomponents need hardly be incorporated. An enlargement of theimpingement spot (“beam footprint”) on the imaging plate can beobtained, for example, by means of an actuator for displacing or curvingthe mirror. But use may also be made, for example, of a displaceablecondenser lens on the laser, or of a diffusing screen that isretractable into the beam path.

The erasing appliance may include an intensity-controlling appliancewith which, for the purpose of erasing the imaging plate, the intensityof the read-out light can be increased. In this way, the samelight-source can be used for erasing that is also utilised for reading,whereby, by virtue of the increase in the intensity, a complete erasureof possibly still excited storage centres is obtained.

Alternatively, the erasing appliance may include a light-source forgenerating erasing light, the erasing light being directed onto thecontrollable mirror, so that with the aid of the deflection unit theerasing light can be directed sequentially onto the imaging plate forthe purpose of erasing the imaging plate. Special erasing light can alsobe used in combination with an enlargement of the impingement spot.

In this case a feed element may have been arranged in the beam pathupstream of the controllable mirror, with which, simultaneously oralternately, the read-out light and the erasing light can be directedonto the controllable mirror.

The erasing appliance may include several sources of erasing light, inparticular light-emitting diodes, which have been arranged around theimaging plate. This is a structurally very simple configuration of anerasing appliance. Preferentially, the sources of erasing light have inthis case been arranged in such a way that the erasing light falls ontothe entire imaging plate.

The sources of erasing light may have been arranged on a side of theimaging plate from which the read-out light falls onto the imagingplate. In this way, both transparent and non-transparent imaging platescan be erased.

The erasing light may have a broader-band spectrum than the read-outlight, as a result of which a higher efficiency of erasure is achieved.

The deflection unit may have been arranged in such a manner that with itthe read-out light can be directed onto a front surface of the imagingplate. The detector unit for fluorescent light has in this case beenarranged in such a manner that with it the fluorescent light emergingfrom a rear surface of the imaging plate can be detected. With such anarrangement, transparent imaging plates can be read, whereby, dependingon the arrangement, the fluorescent light is able to reach the detectorunit directly or indirectly via a reflector.

A supporting plate that is transparent to the fluorescent light may havebeen provided, against which the imaging plate bears. In this way, theimaging plate can be supported on its rear side, without the fluorescentlight emerging there being lost for the measurement. The supportingplate in this case may act as an optical filter that blocks read-outlight and lets fluorescent light pass. By reason of the filter action ofthe supporting plate, only fluorescent light then emerges downstream ofthe supporting plate.

The supporting plate may have a cylindrically curved supporting surfacefor the imaging plate. As a result, at least in one read-out direction aperpendicular incidence of the read-out light onto the imaging plate canbe ensured. In this case a clamping element may have been provided, withwhich the imaging plate is pressed against the curved supportingsurface. A clamping element co-operating with the supporting surface,such as a clamping bracket for example, is a structurally simplearrangement in order to bring the imaging plate into the cylindricalshape.

The supporting plate may also have been constituted by an entrancewindow of the detector unit. Given appropriate adaptation of theread-out region, in this way the imaging plate may bear directly againstthe entrance window of the detector unit and be registered. Particularlyin combination with the filter action, a particularly simple structureof the device arises in this way.

The entrance window in this case may be at least as large as the imagingplate to be read, and may, in particular, have the basic shape thereof.As a result, the entire imaging plate can be registered without thelatter having to be displaced. The size of the entrance window in thiscase may be adapted to the customary standard sizes (size 0, 1, 2 etc.)of the imaging plates.

A supporting frame and a clamping element may have been provided,between which the imaging plate is held, said frame and element havingbeen, in particular, configured and arranged in such a manner that acylindrical curvature is imposed on the imaging plate.

Instead of an uninterrupted supporting plate, only a supporting framemay have been provided, which carries the imaging plate only in marginalregions, in which case both a fully circumferential frame and a framethat is present only intermittently are conceivable. As a result, in thebeam path of the fluorescent light there is still less material thatcould partially absorb or reflect the fluorescent light. The supportingframe may bear against the front side or against the rear side of theimaging plate, in which case the clamping element then undertakes thecorrespondingly complementary function.

With respect to the method, the aforementioned object is achieved by amethod having the following steps:

-   -   a) generating read-out light;    -   b) directing the read-out light on a micromirror;    -   c) directing the read-out light in a scanning movement over the        imaging plate, wherein the micromirror oscillates with a first        frequency about a first swivel axis and simultaneously with a        second frequency, which is distinct from the first frequency,        about a second swivel axis;    -   d) detecting fluorescent light which is emitted from the imaging        plate at locations where the read-out light impinges.

A control unit is able to drive the micromirror about the two swivelaxes at frequencies that correspond to a large, preferentially variable,preferentially integral, multiple of a base frequency, in particular to0.5 times the desired number of lines or the number of columns of theimage, and/or that differ slightly from one another by such an integralmultiple, in particular by 10% of the lower frequency. As a result,patterns are generated that scan the imaging plate completely. Inparticular, the sequential scanning of the imaging plate can be effectedalong a Lissajous figure or curve.

As a result, the micromirror can be driven with a drive signal, thefrequency of which may be at least approximately equal to a naturalfrequency of the micromirror.

The imaging plate may be erased after the scanning, while the imagingplate remains at the location of the scanning. For the purpose oferasing the imaging plate, the intensity of the read-out light can beincreased, and then the imaging plate can be scanned with the aid of thedeflection unit. For the purpose of erasing the imaging plate, animpingement spot of the read-out light falling onto the imaging plate,or of an erasing light falling onto the imaging plate, can be enlarged.

The imaging plate may, in addition, be brought into a cylindrical shapeprior to the scanning.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated below on the basis of embodiments withreference to the drawings. Shown therein are:

FIG. 1 a simplified perspective representation of a scanner for readingimaging plates in accordance with a first embodiment;

FIG. 2 a perspective representation of a micromirror that is used in thescanner;

FIG. 3 a top view of an imaging plate that is being read along a scanpath according to a first mode;

FIG. 4 a top view of an imaging plate that is being read along a scanpath according to another mode;

FIG. 5 a simplified perspective representation of a scanner according toanother embodiment;

FIG. 6 a simplified perspective representation of a scanner fortransparent imaging plates;

FIG. 7 a simplified perspective representation of a scanner fortransparent imaging plates according to an embodiment in which anothererasing appliance and another detector unit are used;

FIG. 8 a simplified perspective representation of a scanner fortransparent imaging plates according to a further embodiment withmodified erasing appliance;

FIG. 9 a simplified perspective representation of a scanner fortransparent imaging plates according to an embodiment in which theimaging plate is carried by a supporting frame.

DESCRIPTION OF PREFERRED EMBODIMENTS First Group of Embodiments

FIG. 1 shows a scanner, denoted overall by 10, for reading an imagingplate 12 which in the form of metastable storage centres excited byX-ray radiation bears a latent X-ray image.

The scanner 10 exhibits a supporting surface 14 for the imaging plate12. For the purpose of fixing the imaging plate 12, the supportingsurface 14 in this case has been provided with a plurality of suctionbores 16 which can have a vacuum applied to them via a vacuum sourcewhich is not shown, so that the imaging plate 12, which is generallyflexible, is able to conform to the supporting surface 14 in flatmanner.

The scanner 10 further includes a laser 18 by way of source of read-outlight, which generates a read-out light beam 20 having a wavelength inthe red spectral region, with which the excited storage centres of theimaging plate 12 can be excited to fluoresce, so that said storagecentres emit fluorescent light 22 which is typically in the bluespectral region.

The laser 18 has been arranged in such a way that it directs theread-out light beam 20 onto a controllable micromirror 24 which has beenarranged on a deflection unit 26. This micromirror 24, which has beenconstructed as a MEMS component, is shown in FIG. 2. Thanks to itscardanic solid-joint suspension 28, it is capable of swivelling abouttwo axes 30 and 32 and can be swivelled continuously about the two axes30, 32 with the aid of capacitive actuators 33 a, 33 b, 33 c, 33 dacting on its underside and with the aid of assigned control circuits ofthe deflection unit 26, which are not shown.

In order to obtain, at least in one direction, a perpendicular incidenceof the read-out light beam 20 onto the imaging plate 12, the supportingsurface 14 in the embodiment shown exhibits a partly cylindricallycurved shape which extends parallel to the swivel axis 30 of themicromirror 24. However, the supporting surface may also have beenconstructed to be completely flat. In addition, an f-theta lens system35 can be provided as needed, which adapts the angle of incidence of theread-out light beam 20 so as to correspond to the shape of thesupporting surface 14.

The laser 18, the supporting surface 14 with the imaging plate 12 andalso the deflection unit 26 with the micromirror 24 have beengeometrically spaced from one another and arranged relative to oneanother in the scanner 10 in such a way that with the aid of themicromirror 24 the read-out light beam 20 is able to scan at least theentire surface area of the imaging plate 12. If the scanner 10 enablesthe reading of variably large imaging plates 12, then, of course, thelargest imaging plate 12 predetermines the total surface area to bescanned.

If it is accepted that, for example, marginal regions of the imagingplate 12 are not read, then the various components may, however, also bearranged in such a manner that by swivelling the micromirror 24 only apartial region of the imaging plate can be scanned.

The scanner 10 further includes a reflector 34, indicated in dottedmanner in the drawing, which encloses the entire measuring space aroundthe imaging plate 12 in light-tight manner, so that the fluorescentlight 22 emanating from the imaging plate 12 is finally reflected to aphotodetector 36. In order to prevent scattered read-out light 20 fromalso reaching the photodetector 36, both the reflector 34 and an inputwindow of the photodetector 36 may have been provided with a dichroicfilter material which blocks or absorbs the read-out light 20 and istransparent to the fluorescent light 22.

For the purpose of controlling the read-out process, the scanner 10includes a control unit 38 and an evaluating unit 40 with a correctionmemory 42, which here have been shown as parts of integratedinstrumental electronics 44, but may also have been implemented ascontrol software on a separate PC. For the purpose of operation, thecontrol unit 38 and the evaluating unit 40 have been connected to adisplay-and-operating unit 46 with which working parameters can beestablished and the image 48 which has been read from the imaging plate12 can be displayed.

The scanner 10 operates as follows:

By swivelling of the micromirror 24 which is controllable about the twoswivel axes 30, 32, the imaging plate 12 is scanned sequentially inpointwise manner with the read-out light beam 20. In the process, theintensity of the emitted fluorescent light 22 is registered with the aidof the photodetector 36 and the evaluating unit 40 and is prepared fordisplay.

The control unit 38 drives the micromirror 24 in such a manner that thelatter executes oscillations about its two swivel axes 30, 32. As aresult of the superposition of the two oscillations, the read-out lightbeam 20 scans the imaging plate 12 along a Lissajous figure (hereinafterLissajous curve) 50 by way of scan pattern. By virtue of the twooscillation frequencies and the relationship thereof to one another, theshape of the Lissajous curve 50 is determined, so that other Lissajouscurve 50 are generated by other frequencies. In the embodiment shown inFIG. 1 the Lissajous curve 50 exhibits four oscillations in thelongitudinal direction and three oscillations in the transversedirection before the scan pattern repeats.

For the purpose of synchronising the evaluating unit 40 with the motionof the read-out light beam 20, one or more photodiodes 51 may have beenarranged in the supporting surface 14 alongside the imaging plate 14.When the read-out light beam 20 roams over these photodiodes 51, thelocation of which is known, the evaluating unit 40 receivescorresponding synchronisation signals.

In order to obtain a high read-out efficiency, the micromirror 24 isdriven at oscillation frequencies that are close to the naturalfrequencies about the two axes 30, 32. The natural frequencies in thiscase are established, inter alia, by the mass of the micromirror 24 andby the angular spring constants of the cardanic solid-joint suspension28.

In order to scan all regions of the imaging plate 12, on the one handvery large frequency ratios, such as 200:1 for example, can now beselected, so that the scanning, as indicated in FIG. 3, correspondsvirtually to a line-by-line scanning, in the course of which a slowmotion of the read-out light beam 20 occurs along one direction, whereasin the other direction several panning motions follow one anotherrapidly. In the process, the controllable micromirror 24 can be drivenwith an oscillation amplitude at which the read-out light beam 20 runsbeyond the edges of the imaging plate 12. In this way, the regions ofthe reversal-points, in which the read-out light beam 20 lingers for arelatively long time, are displaced into regions outside the imagingplate 12, as a result of which an even more uniform scan pattern ariseson the imaging plate 12.

However, the frequency ratios of the two oscillations can also easily bedetuned in relation to one another, for example in a ratio 3:4.05, sothat the lines of the Lissajous curve 50 are easily displaced upon eachsweep of the figure and in this way a moving Lissajous curve 50 isgenerated which gradually scans all regions of the imaging plate 12.This procedure is indicated in FIG. 4, in which the initial regions ofthe first, second and third sweeps of the Lissajous curve 50 have beenindicated respectively by 52, 54 and 56.

Since with this method the imaging plate 12 is scanned repeatedly atmany points, for example at the points of intersection of the Lissajouscurve 50, and, in the process, excited storage centres possibly stillremaining additionally emit fluorescent light 22, the evaluating unit 40has to take this into account appropriately in the course of evaluatingthe photodetector signal and in the course of building up the image.

To this end, for the purpose of calibration a completely uniformlyexposed imaging plate 12 may be used which is scanned with the Lissajouscurve 50 provided for the purpose of read-out. In the process, thesignals received from the photodetector 36 are added up, whereby, byreason of the multiple scanning of the points of intersection, brightersummed intensities arise in the image 48 at these points. Thecalibration image 48 obtained in this way is converted into correctionvalues which are saved in the correction memory 42 of the evaluatingunit 40. If subsequently an imaging plate 12 is read that containsactual image information, the ascertained intensities are corrected soas to correspond to the correction values contained in the correctionmemory 42.

For calibration purposes, mathematical methods are also conceivable inwhich the scanning path of the Lissajous curve 50 is modelled and takeninto account appropriately in the course of the summation of thephotodetector signal. Also in this way, the effects of the multiplescanning or of the variable speeds of motion along the scan pattern canbe compensated, and correction values can be ascertained which are savedin the correction memory 42. However, with these purely mathematicalmethods special properties of the plate, for example what percentage ofthe excited storage centres still remains after a first read-outprocess, can only be taken into account if the type of imaging plate isspecified by the operator or by an automatic recognition system.

FIG. 5 shows a scanner 110 according to another embodiment, whereinstructurally similar components bear reference symbols increased by 100.

In the embodiment shown in FIG. 5, instead of the micromirror 24 amicromirror array 124 has been provided on the deflection unit 126, inwhich the individual micromirrors 125 can be switched in binary mannerbetween two positions of tilt. Micromirror arrays 124 of such a type areused in the field of consumer electronics in DLP projectors forgenerating projected images and are available on the market in largenumbers at favourable cost.

In order to illuminate the entire micromirror array 124, the read-outlight beam 120 emanating from the laser 118 is expanded via an expandinglens system 160. By switching the individual micromirrors 125, componentbeams 121 of the read-out light beam 120 can then be directed eitheronto the imaging plate 112 or onto a beam absorber 162 which absorbs thecomponent beams 121. For this purpose the beam absorber 162 may havebeen constructed to be strongly absorbing.

The scanner 110 operates in such a way that in each instance only one ofthe micromirrors 125 of the micromirror array 124 has been set to “ON”,i.e. the associated component beam 121 thereof has been directed onto apoint assigned to it on the imaging plate 112. All other micromirrors125 have at this time been set to “OFF”, i.e. the component beams 121thereof are directed onto the beam absorber 162. In this way, theimaging plate 112 can be scanned, point by point, by pointwise switchingof the micromirrors 125 on and off.

In a modification, the micromirror 24 may be capable of being swivelledabout only one swivel axis 30. In this case the supporting surface 14can, as indicated in FIG. 1 by the double-headed arrow A, be moved alongone direction, preferentially axially along the cylindrical shape of thesupporting surface 14, in order to move the imaging plate 12 past theread-out line constituted by the swivelling read-out light beam 20. Butthe supporting surface 14 can also be moved in the case where use ismade of the biaxial micromirror 24 if particularly large-area imagingplates 12 have to be read.

In a further modification, the micromirror 24 may also be driven instepwise manner, so that the micromirror 24 can remain in individualintermediate positions of tilt, allowing a read-out, pixel by pixel, ina matrix. As a result, the read-out beam is able to dwell at each pointof the imaging plate 12 for a desired read-out time, whereby each pointcan then also be read out for an equally long time. This has the resultthat each point of the registered image exhibits the samesignal-to-noise ratio.

Second Group of Embodiments

FIGS. 6 to 9 show embodiments with alternative arrangements of thedetector unit, and various options for erasing the imaging plate afterthe latter has been read. Structurally similar components in these casesbear reference symbols increased respectively by 200, 300, 400 and 500with respect to those used in FIG. 1. In order to simplify FIGS. 6 to 9,the instrumental electronics 44 have not been shown in these Figures.

FIG. 6 shows a scanner 210 with which an imaging plate 212 that istransparent to fluorescent light can be read.

The scanner 210 includes for this purpose a photodetector 236, theentrance window of which is constituted by a filter plate 237 whichblocks the read-out light 220 but lets the fluorescent light 222 pass.The photodetector 236 has furthermore been arranged in such a way thatthe surface of the filter plate 237 pointing outwards serves at the sametime as supporting surface 214, against which the imaging plate 212bears. The imaging plate 212 is consequently arranged directly in frontof the entrance window of the photodetector 236.

During the read-out process the read-out light 220 impinges from oneside onto the imaging plate 212. The fluorescent light 222 released inthe process then emerges on the other side of the imaging plate 212, inorder to get from there through the filter plate 237 and into thephotodetector 236 and to generate a signal therein. The filter action ofthe filter plate 237 prevents the read-out light 220 from alsogenerating a signal in the photodetector 236.

In order to erase an imaging plate 212 completely that has already beenread, in the case of the scanner 210 a displaceable condenser lens 266,an erasing-light source 268 and a feed element 270 have been provided byway of erasing appliance. With the feed element 270 both the read-outlight 220 of the laser 218 and the erasing light 267 of theerasing-light source 268 feed into the beam path that leads to thedeflection unit 226.

For the purpose of erasing the imaging plate 212, the condenser lens 266is displaced in such a way that the impingement spot of the read-outlight 220 or of the erasing light 267 on the imaging plate 212 isenlarged. After this, the imaging plate 212 is scanned until such timeas a sufficiently complete erasure of excited storage centres stillremaining can be assumed.

The use of broader-band erasing light 267 is not absolutely essential inthis case. Accordingly, under certain circumstances it may suffice toincrease the intensity of the read-out light 220 emitted by the laser218 with the aid of the intensity-controlling unit 269, and to carry outthe erasure with this read-out light. In this case the erasing-lightsource 268 and the feed element 270 can be dispensed with.

FIG. 7 shows a scanner 310 in which a separate erasing-light source 368has likewise been provided. However, the light of the erasing-lightsource 368 is not fed into the same beam path as the read-out light 320but is directed onto the micromirror 324 of the deflection unit 326 atan angle differing from that of the read-out light 320.

For the purpose of erasure, the micromirror 324 is then driven by thecontrol unit 338, taking a corresponding offset angle into account, insuch a way that the erasing light 367 falling onto the micromirror 324from a direction differing from that of the read-out light 320 isnevertheless directed onto the imaging plate 312.

Furthermore, the scanner 310 exhibits a detector unit 336 which exhibitsa rectangular entrance window, the size and shape of which correspondroughly to those of the imaging plate 312.

The embodiment shown in FIG. 8 shows a scanner 410 in which the filterplate 437 exhibits a cylindrically curved supporting surface 414 ontowhich the imaging plate 412 is placed with the aid of a clamping element439. The radius of curvature of the supporting surface 414 correspondsin this case to the spacing thereof from the micromirror 424, so that inthe transverse direction relative to the cylinder axis the read-outlight 420 always falls perpendicularly onto the imaging plate 412,regardless of the deflection angle.

In the axial direction of the supporting surface 414 a perpendicularincidence on the imaging plate 412 can be generated via an f-theta lenssystem acting uniaxially. However, if a deterioration of the read-outquality in the axial direction, occurring by virtue of variable obliqueincidence, is accepted, then an f-theta lens system can be dispensedwith completely.

For the purpose of erasing the imaging plate 412 completely, in thisembodiment an LED strip 472 with erasing-light LEDs 474 has beenprovided by way of erasing appliance, which has been arrangedcircumferentially above the filter plate 437 in such a way that theuniformly spaced erasing-light LEDs 474 are able to direct their erasinglight 467 onto the imaging plate 412.

Finally, FIG. 9 shows an embodiment of a scanner 510 in which acylindrically curved supporting frame 576 has been provided for atransparent imaging plate 512. A clamping frame 578 co-operates with thesupporting frame 576, so that the imaging plate 512 introduced betweenthe supporting frame 576 and the clamping frame 578 is keptcylindrically curved.

In order to keep the scanner 510 as compact as possible, the latterfurther includes a reflector mirror 580 which here has been constructedin curved manner and which has been arranged with respect to thesupporting frame 576 on the side situated opposite the micromirror 524.The reflecting mirror 580 and the photodetector 536 have furthermorebeen arranged relative to one another in such a way that fluorescentlight 522 emerging on the imaging plate 512 from the reverse sidethereof falls onto the entrance window of the photodetector 536 afterreflection on the reflector mirror 580. By reason of the reflectormirror 580, the position of the photodetector 536 can be chosen morefreely, enabling a more compact structural shape of the scanner 510. Inaddition, a photodetector 536 with a smaller entrance window can be usedif the reflector mirror 580 has a focusing action.

What is claimed is:
 1. A device configured to read an exposed imagingplate, the device comprising a light source configured to generateread-out light; a deflection unit configured to direct the read-outlight in a scanning movement over the imaging plate, wherein thedeflection unit comprises a micromirror configured to deflect impingingread-out light towards the imaging plate, and wherein the micromirror isconfigured to swivel about a first swivel axis and about a second swivelaxis that is distinct from the first swivel axis; a detector unitconfigured to detect fluorescent light, which is emitted from theimaging plate at locations where the read-out light impinges; and anevaluating unit configured to evaluate signals received from thedetector unit and to build up an image that is stored in the imagingplate, wherein the evaluating unit is further configured to take intoaccount, when evaluating the signals received from the detector unit,that points on the imaging plate are subjected to the read-out lightvariably often and/or for variable time lengths while the micromirroroscillates about the first and the second swivel axis.
 2. The device ofclaim 1, further comprising a control unit that is configured to excitethe micromirror such that the micromirror oscillates with a firstfrequency about the first swivel axis and simultaneously with a secondfrequency, which is distinct from the first frequency, about the secondswivel axis.
 3. The device of claim 2, wherein the first frequency is atleast 250 times as large as the second frequency.
 4. The device of claim2, wherein the control unit is configured to control the micromirrorsuch that the read-out light follows a Lissajous figure on the imagingplate.
 5. The device of claim 4, wherein the Lissajous figure isdetermined such that the imaging plate is completely scanned.
 6. Thedevice of claim 1, wherein the evaluating unit is configured to takeinto account, when evaluating the signals received from the detectorunit, that points on the imaging plate are subjected to the read-outlight variably often and/or for variable time lengths while themicromirror oscillates about the first and the second swivel axis, byusing a position dependent correction factor.
 7. The device of claim 6,wherein evaluation unit is configured to retrieve the position dependentcorrection factor from a correction table stored in a correction memory.8. The device of claim 6, wherein the correction factor is obtained froma calibration process.
 9. The device of claim 6, wherein the correctionfactor is obtained from a simulation.
 10. The device of claim 1, furthercomprising an erasing appliance that is configured to direct erasinglight onto the imaging plate, after the reading of the imaging plate, inan erasing region, wherein the erasing appliance comprises a switchingelement, which is configured to enlarge a spot that is produced by theread-out light on the imaging plate, and an intensity-controllingappliance configured to increase an intensity of the read-out light forthe purpose of erasing the imaging plate.
 11. The device of claim 2,wherein the control unit is configured to control the micromirror suchthat reversal-points of oscillations of the read-out light are arrangedoutside the imaging plate.
 12. The device of claim 1, further comprisinga supporting plate that is transparent to the fluorescent light andagainst which the imaging plate bears.
 13. The device of claim 12,wherein the supporting plate acts as an optical filter, which blocks theread-out light and lets fluorescent light pass.
 14. A method of readingan imaging plate, the method comprising the following steps: a)generating read-out light; b) directing the read-out light on amicromirror; c) directing the read-out light in a scanning movement overthe imaging plate, while the micromirror swivels about a first swivelaxis and simultaneously about a second swivel axis that is distinct fromthe first swivel axis; d) detecting fluorescent light which is emittedfrom the imaging plate at locations where the read-out light impinges;e) evaluating signals received from the detector unit to build up animage that is stored in the imaging plate; wherein during step e) takinginto account that points on the imaging plate are subjected to theread-out light variably often and/or for variable time lengths while themicromirror oscillates about the first swivel axis and the second swivelaxis.
 15. The method of claim 14, wherein the micromirror is oscillatedwith a first frequency about the first swivel axis and simultaneouslywith a second frequency, which is distinct from the first frequency,about the second swivel axis.
 16. The method of claim 15, wherein thefirst frequency is at least 250 times as large as the second frequency.17. The method of claim 14, wherein the control unit controls themicromirror such that reversal-points of oscillations of the read-outlight are arranged outside the imaging plate.
 18. The method of claim17, wherein a portion of a pattern, along which the read-out lightfollows during the scan movement, extends beyond an edge of the imagingplate by a length that is between 5% and 15% of a length of the imagingplate perpendicular to the edge.
 19. The method of claim 14, wherein theread-out light follows a Lissajous figure on the imaging plate.
 20. Themethod of claim 14, wherein during step e) the taking into account thatpoints on the imaging plate are subjected to the read-out light variablyoften and/or for variable time lengths while the micromirror oscillatesabout the first and the second swivel axis is by using a positiondependent correction factor.
 21. The method of claim 20, wherein theposition dependent correction factor is retrieved from a correctiontable stored in a correction memory.
 22. The method of claim 20, whereinthe correction factor is obtained from a calibration process.
 23. Themethod of claim 22, wherein, during the calibration process, acompletely uniformly exposed imaging plate is scanned and signalsreceived from the detector are added up so as to obtain a calibrationimage, which is then converted into correction factors.
 24. The methodof claim 20, wherein the correction factor is obtained from asimulation.